Mifsud and Alok Sharma, the MP for Reading West and a Foreign Office minister met several times including late October 2017 fundraising dinner attended by Boris Johnson to discuss Brexit

Foreign Office Minister Tobias Ellwood, met Papadopoulos at the UN general assembly in September 2016

“In Britain, on 25 April 2016, the news was dominated by the forthcoming vote. “EU referendum: Boris Johnson claims ‘elites want to remain in Europe to keep hold of power’”said the headline in the Independent.”

The charges filed against a Trump aide shocked the US – but also shed new light on the complex connections that link Russia to Brexit and the Foreign Office

The Russian ambassador to the UK, Alexander Yakovenko, left, with Joseph Mifsud at the Russian embassy.“Last weekend, the Observer asked why Nigel Farage has not been questioned about his connections to the Trump-Russia investigation, particularly regarding his relationship to Julian Assange, whose WikiLeaks website published thousands of internal Democratic party emails in the run-up to the US election. But last week’s revelations introduce a whole new cast of characters. And at the centre of it all is London – this “neutral city” – playing the same strategic role that Vienna did during the cold war.

Alok Sharma: met Mifsud several times. Photograph: Lewis Whyld/PA

“The entire city is a nest of spies,” a British intelligence source told the Observer this year. “There’s more espionage activity here now than there was even at the height of the cold war.”

On 25 April 2016, the world had no clue about Papadopoulos, about Trump and Russia, or about the man quickly identified as the “London professor” – a 57-year-old Maltese academic, Joseph Mifsud. Reached by journalists, Mifsud confirmed that the US indictment refers to him but denied any knowledge of its claims about links to the Kremlin, or of knowing about “dirt on Hillary” in “thousands of emails”.

But what the document does not spell out – and what the Observer has learned – is that both Mifsud and Papadopoulos also had links into the heart of the British government.

We publish evidence today of several confirmed meetings betweenMifsud and Alok Sharma, the MP for Reading West and a Foreign Office minister until June this year. It was this relationship between Mifsud and Sharma that put the “London professor” directly into the orbit of the foreign secretary, Boris Johnson, two weeks ago – at a fundraising dinner attended by both Johnson and Mifsud, with Mifsud telling a colleague he was returning to London from Rome to “have dinner with Boris Johnson … re Brexit”.

The Foreign Office has confirmed that a third minister, Tobias Ellwood, met Papadopoulos at the UN general assembly in September 2016. Ellwood ignored multiple attempts by the Observer to contact him and has refused to comment on how the contact was made or what was discussed.

Three Foreign Office ministers approached in three different ways. Yet when asked last week if there was any evidence of Russian interference in British politics, Johnson said: “I haven’t seen a sausage.”

Johnson cannot have been looking very hard. He is far from the first senior politician to be targeted – a group that includes some of his closest colleagues in the Leave campaign. Because what the Observer and Guardian’s investigation into foreign influence in the EU referendum is starting to reveal is that the tentacles of US influence and money, and Russian influence and money, reach much deeper and further into the British political establishment than we have yet understood.

In Britain, on 25 April 2016, the news was dominated by the forthcoming vote. “EU referendum: Boris Johnson claims ‘elites want to remain in Europe to keep hold of power’”said the headline in the Independent. The referendum was less than two months away and Johnson was the figurehead of the official Vote Leave campaign.

The surprise announcement last week from the Electoral Commission of an inquiry into “the true source of donations” to Leave campaigners is focused on Arron Banks – the main donor behind Farage’s fringe Leave.EU campaign. But Johnson was at the head of the “official” campaign – the commission designated Vote Leave as the government-approved campaign, an honour that meant it got to spend £7m, including £600,000 of taxpayers’ money. And although he was still mayor of London, Johnson was Vote Leave’s show pony – the charismatic figurehead who led from the front.

He was not the legal head of the campaign. That was Matthew Elliott, 39, a political strategist who had registered Vote Leave Ltd at Companies House and filed the legal documents with the commission. In 2004, Elliott had founded the TaxPayers’ Alliance, a rightwing pressure group advocating low taxes and minimal government, and he had worked his way up the political ladder to win one of the most coveted and responsible jobs of 2016: chief executive of Vote Leave.

If Johnson wanted to understand how the Russian government had deliberately targeted British political figures and spent years cultivating relationships with key individuals, he could have looked to the man responsible for leading his own campaign.

Matthew Elliott, the former head of Vote Leave, was also a member of Conservative Friends of Russia. Photograph: Peter Nicholls / Reuters/Reuters

In 2012 – or possibly earlier – Matthew Elliott was targeted by a man the Home Office now believes was a Russian spy. Sergey Nalobin was the first secretary in the Russian embassy’s political section in London when Elliott met him – a man who, according to a Daily Telegraph report, “was tasked with building relations with MPs [and] a regular fixture on the Westminster drinks circuit and at political party conferences”.

Nalobin was also a man who, in August 2015, had his permission to stay in Britain suddenly revoked. The Home Office refused to renew the visas of four Russian diplomats, normally a rubber-stamping exercise, Nalobin among them. The timing was not a coincidence: a week earlier, the inquiry into the death of Alexander Litvinenko concluded he was “probably murdered on the personal orders of Putin”.

Nalobin had long been a person of interest. In 2012, he was the key figure at the heart of an organisation called Conservative Friends of Russia, a high-profile new group that threw a high-profile launch in the Russian ambassador’s garden – the same ambassador, Alexander Yakovenko, who was named last week in the FBI documents – and that attracted the endorsement of senior politicians including, initially, Malcolm Rifkind, until he resigned. Rifkind was then chair of the Commons intelligence and security committee.

But the Conservative Friends of Russia was not what it seemed, and nor was Nalobin. A series of reports by the Guardian’s Luke Harding and others revealed that Nalobin was intimately connected to the FSB, and that the Conservative Friends of Russia was a Moscow influence operation.

Sergei Cristo, a Russian-born financier and long-time Conservative activist who helped expose the organisation, told the Observer last week how he was targeted first by Nalobin but quickly became aware that there was something very wrong. “He was trying very hard to find an entry route into the Conservative party, and initially he thought that would be me. I met with him several times and he told me how he could help with fundraising. He said: ‘We have companies. We have Russian companies here in London willing to donate to the party.’ I knew this was illegal, of course. I went away thinking, ‘I wish I was wired.’”

This, he said, was about six months before the group’s launch.

Boris Johnson: at a fundraising dinner that Mifsud also attended two weeks ago. Photograph: Neil Hall/Reuters

Cristo reveals an even more extraordinary detail – a detail that he first told to a journalist in 2013 so which has not been inflected by more recent events: “The most pressing question Nalobin asked was whether or not there really was a personal rivalry between David Cameron and Boris Johnson.”

At the time, Cristo thought, “it was completely trivial”. “It was all chatty, chatty, chatty. It was only question he pressed me on. ‘Do you think it’s personal?’ he kept on asking.

“I think he was trying to work out if it was a deep-seated alpha-male-type thing. I do wonder now if they were looking to exploit that antipathy even way back then. It’s very interesting, given the crucial role that Boris played in Brexit.”

Matthew Elliott has never made his association with the Conservative Friends of Russia public. In 2012, he was not publicly known. Since the referendum, he has launched a new organisation, Brexit Central, and the Times reported last week that he was being lined up for a senior role at the head of the party – most likely vice-chairman, as a reassuring “signal of intent on Brexit” for the hardliners.

But photographs from 2012 reveal that he was a founding member of the group and later that year went on a 10-day trip to Moscow with all expenses paid by the Russian government. No names were ever released but on 11 September, Elliott tweeted: “New photos on my Facebook page from my recent trip to Moscow, here’s a teaser! Back to the grind …”

Most extraordinary of all, when he announced his engagement on Twitter on 10 January 2014, the first person to congratulate him was Sergey Nalobin. “@matthew_elliott @SarahBSmithVA congratulations, guys! All the best in the long-long journey.” Sarah Smith – now Elliott’s wife – responded warmly: “thank you!! I’m excited to have a great partner next to me :)”

Just over 18 months later, Nalobin was “expelled” from Britain. And yesterday, Elliott declined to answer any questions from the Observer about his relationship with Nalobin or Conservative Friends of Russia. He declined also to explain the nature of the political work he claims to have done in Ukraine in some official biographies.

Did Johnson know of Elliott’s connections to a Russian operative? Probably – because he also knew Nalobin. They are photographed at Russian embassy events together. Did the British intelligence services? An intelligence source told the Observer of “enormous sensitivity” around any investigation of politicians. And Elliott was not an MP, but in 2016 he did hold an official position – designated by an official body, the Electoral Commission. Was his relationship to Nalobin flagged by the security services? If so, by whom, to who? If not, why not?

Will the FBI’s revelations last week finally shine some light on Russia’s relationship with Britain? And if so, what else will we find out? Because it is clear that the relationships and meetings the Observer has uncovered between Papadopoulos, Mifsud and British ministers are likely to be the tip of the iceberg.

Which other ministers were contacted? Who else met them? Are the Conservatives, and indeed other parties, ready to start examining their relationships with Russian individuals and companies, going back years? And who is going to take a stand and force Facebook, Google and Twitter to face parliament and start answering questions?

Bill Browder, an Anglo-American businessman who is leading a global campaign for a “Magnitsky Act” – aimed at punishing Russia for the murder of his lawyer, Sergei Magnitsky, in Moscow in 2009 – said he was unsurprised by Britain’s role.

“London is one of the main outposts for Russian financial and political influence programmes in the west. It’s floating on a tide of dirty money. All the oligarchs have bases there. They all have homes. All the professional service firms are in London – lawyers, investigations agencies – all running private influence ops on behalf of the oligarchs who are working on behalf of Putin. There’s a huge reluctance in Britain to strangle the golden goose. Because a lot of people very close the centre of power are financially benefiting.”

The question is who? And how? Speaking to the Observer about the inquiry into the sources of funds for his Leave.EU campaign, Banks complained about the focus on him. “There should be an inquiry into all the campaigns, not just us.” And later: “What about Vote Leave?”

Sergey Nalobin: expelled in 2015.

What about Vote Leave? And what about the new man in the Russian embassy? Some of the suspicion that has encircled Banks has been a result of his Russian wife, Katya, his vocal support of Putin, and the fact that in his memoir, The Bad Boys of Brexit, he is quite open about his Russian contacts, describing how he met a man called “Oleg” in Doncaster at the Ukip conference.

“He was introduced to us as the first secretary at the embassy – in other words, the KGB’s man in London.” “Oleg” then introduced him to a figure now of significant interest to the FBI – Alexander Yakovenko, the Russian ambassador to London.

Ukip’s power is all but spent in Britain. It is the Conservatives who now hold the keys to the kingdom. And Sergei Cristo tells me he met another senior Russian diplomat at this year’s Conservative party conference.

Cristo is not a man out to discredit the Conservatives. He is a committed supporter of the party. But he’s also a close friend of Marina Litvinenko, the widow of the man murdered on Putin’s orders. The problem, he says, is that so many MPs and party officials are “hopelessly naive and uneducated” on the subject of Russia.